The present invention relates to boilers; and particularly to apparatus for chemically treating of water used in boilers.
Large boilers, such as those used in commercial buildings, super heat water which then flows under pressure to an appliance where the pressure is reduced to convert the water to steam. The appliance may be a radiator for heating the building, an autoclave for sterilizing hospital instruments, or laundry equipment. In many cases, the steam condenses to liquid form in the appliance and the condensate is returned to a feed tank which supplies water to the boiler. The water cycles through the system in this manner.
In some appliances the steam is vented to the atmosphere and little water returns from the appliance to the feed water tank. To make up for the water lost from the system in this manner, water from a well or municipal water supply is added as needed to the feed water tank. Typically a float valve in the tank opens to add the water when the level in the tank drops below a given point.
When the steam is created minerals present in the super heated water remain in the condensate. As the steam leaves the system and is replaced by water from a supply, the concentration of minerals and other dissolved solids in the system increases. Periodically, an outlet valve on the boiler is opened to drain a portion of the water with a high concentration of dissolved solids. This fluid loss also is replenished by fresh water from the supply causing the concentration of dissolved solids in the boiler water to diminish. The draining process is commonly called a "blow down". Conventional systems for automatically controlling the blow down measure the electrical conductivity of the water and open the drain valve when the conductivity exceeds a threshold level which corresponds to an undesirably high concentration of total dissolved solids.
The internal components of the boiler may corrode over time depending upon the acidity of the water from the supply. To counter this effect, a corrosion inhibitor is added to the boiler water and must be replenished in order to maintain the proper concentration as water escapes.
It is therefore desirable to provide an automatic control system for blowing down the boiler when the concentration of total dissolved solids becomes excessive. The control system also should add chemicals as needed. However, in order to reduce operating expenses, the addition of chemicals must be regulated so that only the amounts necessary for satisfactory operation are added to the boiler. It is also desirable that the accuracy of the system be periodically checked and an indication given to the operator when maintenance is required, such as cleaning the conductivity sensor.